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It is a double decker version of the other one, about 1/3 the air flow

You can see the chilled water connections on the ass end of it. Inside there is a DX coil and a reheat coil like the other unit also.

The return (mixed air) connection is on the lower end, the supply upper end. I guess like an over and under.

A chilled water coil pulls mixed air down in the 52 to 54F range, but when we need more dehumidifying the DX coil in the above picture cools the air down under 49F.

All the drain pans are stainless, the paint sort of hides that, but the drains are on the bottom and then come out of the rail. No standing water in this one well I guess if there is some carry over off the coil it could get as high as the welds

Last edited by Carnak; 11-21-2009 at 03:51 PM.

The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

A plenum fan with a premium efficiency 7.5 HP motor pulls air through an external filter bank, and then through a chilled water coil then a DX coil.

The fan discharges the cooled air up into a plenum on the upper level that turns the air. The air goes through the DX condenser coil to get reheated and then out the end to an external HEPA filter bank.

When the filters are about half loaded with dirt, the fan will develop over 7 inches of static. The blower section and then the plenum section up top are under pressure.

If you are dumb enough not to shut the fan off, as long as your face is 4 inches from the unit, you will not get punched in the head.

You open the door handle once and there is still a safety hook that will catch the frame. You have to open the door handle, pull the door open a couple inches then close the handle to get the hook clear of the frame.

Built in compressor section. On a dehumidification call this unit will blow 68F dry air into the space.

The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

Usually it is easier to have two different pieces of equipment (two fans) for the two requirements for such an application. One has the filters and fan to meet the air rotation part and the other is the machine to satisfy the load part. That helps reduce the coil size and needs a smaller fan for that part. This system may have a problem holding the temperature to within +/- 5 degree and the humidity to within +/- 10% rh because there is only one stage. You should have four stages reduce the over capacity requirement when tracking a demand curve for such an application. It would help the energy consumption to have either a fixed plate heat-exchanger or a total enthalpy desiccant wheel so that you don't depend on the refrigeration system entirely without reclaiming anything.

Even a two stage cooling system will use 30% to 40% more energy than a four stage system when tracking a load curve. The graphs are attached.

if it was new construction, perhaps a fixed plate renewair type of enthalpy device. Space was pretty tight, that is why it was built as a double decker and 'over and under'

Sometimes you need the reheat because it is pyschrometrically impossible to supply the air you need without it. So in addition to hot gas reheat, there is a few degrees of fan heat helping out as well.

The main coil is chilled water, so quite a bit of modulation possible, but I really only need to drop it by two degrees if there is some kind of huge latent spike.

The chilled water coil is trying to cool mixed air down to 54F , it will be close to fog, so will have a dewpoint just under 54. When keeping a space at 68F, a dewpoint just under 54 means 60% RH.

I am actually finding it easier to maintain RH under 40% than to keep it tight at 55%.

Holds temperature pretty good, within 2F at the moment. Need a couple more phases complete to get it rock solid steady.

Think about it, I am keeping a space at 68F, when it gets too humid and temp is fine, it blows 68F dry air. If it starts warming up a bit, shut off the DX.

The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

Sweet dew dropper

Thanks for the display. Is it possible to post the psych plots of your problem and resolution?

whenever an air conditioner starts up, it is very inefficient. Once you have it running, you want it to keep it running as long as you can.
John Proctor"Christ is the Son of God Who died for the redemption of sinners and was resurrected after three days. This is the greatest truth in the universe. I die because of my belief in Christ." Watchman Nee